1. Field of the Invention
The present invention relates to a photosensitive composition which is useful in the manufacturing step of a semiconductor such as IC, the manufacture of a circuit board such as liquid crystals and thermal heads, and other fabrication steps and to a method for forming a pattern using the same. More specifically, the invention relates to a photosensitive composition which is suitable in the case of using far ultraviolet light of not more than 220 nm or the like as an exposure light source or using electron beams or the like as an irradiation source and to a method for forming a pattern using the same.
2. Background Art
A chemical amplification type photosensitive composition is a pattern forming material in which radiations such as far ultraviolet light are irradiated to generate an acid in the exposed area, a reaction using this acid as a catalyst changes solubility in a developer between an active radiation-irradiated area and a non-irradiated area, and a pattern is formed on a substrate.
In the case where KrF excimer laser is used as an exposure light source, since a resin comprising poly(hydroxystyrene) as a basic skeleton and having small absorption mainly in a region of 248 nm is used as the major component, the resulting system has high sensitivity and high resolution and can form a good pattern and becomes a good system as compared with the related art naphthoquinonediazide/novolak resin system.
On the other hand, in the case of using a light source with a shorter wavelength, for example, ArF excimer laser (193 nm), as an exposure light source, since a compound having an aromatic group exhibits large absorption substantially in a region of 193 nm, even the foregoing chemical amplification system was not satisfactory yet.
For that reason, there have been developed resists for ArF excimer laser containing a resin having an alicyclic hydrocarbon structure.
Furthermore, it has been found that a performance is enhanced by containing a repeating unit having a lactone structure in the foregoing resin having an alicyclic hydrocarbon structure. Patent Document 1 (JP-A-9-73173) and Patent Document 2 (U.S. Pat. No. 6,388,101B) describe resist compositions using a resin containing a repeating unit having a mevalonic lactone structure or a γ-lactone structure; and Patent Document 3 (JP-A-2000-159758), Patent Document 4 (JP-A-2001-109154), and Patent Document 5 (U.S. No. 2001-26901A) describe resist composition using a resin containing a repeating unit having an alicyclic lactone structure.
However, it is the actual situation that from the viewpoint of overall performance as a resin, it is extremely difficult to find out an adequate combination of a resin, a photo-acid generator, additives, a solvent, and so on to be used. Furthermore, in forming a fine pattern having a line width of not more than 100 nm, improvements in not only a resolution but also a line edge roughness performance of line pattern were required.
The “line edge roughness” as referred to herein means that an edge at the interface between a line pattern of the resist and a substrate exhibits a shape such that it fluctuates irregularly in the vertical direction against the line direction due to characteristics of the resist. When this pattern is observed from directly above, the edge is seen unevenly (from approximately ± several nm to several tens nm). Since this unevenness is transferred onto the substrate by an etching step, if the unevenness is large, failure of electric characteristics is caused, leading to a reduction of the yield.